Hydrazine solutions of hydrazinium polyhydrododecaborates and their preparation



United States Patent 3,228,814 HYDRAZINE SOLUTIONS OF HYDRAZINTUMPOLYHYDRODODECABORATES AND THEIR PREPARATION William A. Jenkins,Wilmington, DeL, Walter H. Knoth,

Jr., Mendenhall, Pa., and Henry S. Rothrock and Robert A. Smiley,Wilmington, Del., assignors to E. I. du Pont de Nemours and Company,Wilmington, DeL, a corporation of Delaware No Drawing. Filed May 7,1962, Ser. No. 193,655 11 Claims. (Cl. 149-22) This invention relates tocompositions containing boron and nitrogen. More particularly, itrelates to compositions containing hydrazines and selected boroncompounds, and their preparation.

Compositions containing hydrazine and low molecular weight boroncompounds are useful as liquid monopropellants for rocket propulsionmotors. However, the compositions now available are deficient in one ormore characteristics and they do not perform as well as desired. A needexists, for example, for compositions which combine superior stabilityduring handling and storage with the property of releasing largequantities of energy at controllable rates.

It is an object of the present invention to provide boron-containingcompositions which have excellent stability, particularly againstpremature thermal or oxidative decomposition and which are useful asliquid base fuels.

The compositions of the present invention are mixtures comprising ahydrazine and a hydrazinium polyhydrododecarborate 2) The termhydrazine, as used herein, refers to a compound of the general formulaRRNNH wherein R and R are hydrogen or lower alkyl groups, e.g., methyl,ethyl, propyl, butyl, and the like.

The term hydrazinium polyhydrododecarboate(2-) refers to a hydrazinesalt of a divalent anion of 12 conjointly bonded boron atoms each ofwhich is singly bonded to a monovalent element or group of elementswhich form a monovalent substituent.

In its simplest form, the polyhydrododecarborate anion is represented asB H However, one or more of the hydrogens on the dodecarborate cage canbe replaced with substituents which are monovalent elements ormonovalent groups, e.g., OH, NH and the like. Preferably,

substituents on the dodecarborate cage, if present, are

groups which may improve the solubility of the hydrazinium salts in ahydrazine. The dodecaborates, whether substituted or unsubstituted, aredivalent anions which combine with 2 moles of a hydrazine to form adihydrazinium salt.

The preferred compositions of the invention are fluid mixtures orsolutions consisting principally of a hydrazine of the formula RR'NNHand a hydrazinium dodecahydrododecarborate(2) of the formula where R andR are hydrogen or lower alkyl groups.

Especially preferred compositions, for reasons of cost and availabilityof components, are solutions whose principal components are hydrazine(NH NH and dihydrazinium dodecahydrododecarborate(2) 3,228,8l4 PatentedJan. 11, 1966 components constitute the principal portion of thecompositions, i.e., at least by weight of the total composition. Minoramounts of other components can be present, in particular, componentswhich function as freezing-point depressants, e.g., water, hydrogensulfide, hydrogen cyanide, and the like. However, these components donot constitute the novel and characterizing feature of the compositionsof the invention.

The compositions are clear solutions which are liquids at normalatmospheric temperatures. They are stable when heated in air forprolonged periods, e.g., the solutions can be heated at -100 C. forseveral hours (two or more hours) in containers exposed to the air withno evidence of decomposition. The solutions can be stored withoutdegradation in conventional containers customarily used for hydrazines.

Solutions which contain about 35% or more by weight of the hydrazinesalt in substantially pure hydrazine may form deposits on cooling butthese deposits may be redissolved by adding small quantities of water orother solvents, or by heating the solution.

The compositions of the invention provide hydrazine solutions which havea high boron content and, therefore, a high boron/nitrogen ratio. Toillustrate, a solution of about 25% by weight of (NI-l NH B H inhydrazine contains l5-16% of boron. In contrast, a solution of about 25by weight of a hydrazinium salt of a lower hydroborate, e.g., NH NH BHcontains only about 6% by weight of boron. A further advantage of thecompositions of the invention lies in the high rate of combustion ofhydrazinium salts of polyhydrododecarborate anions, especially the B Hanion. This property permits the release of large quantities of energyunder readily controlled conditions. Compositions derived from salts ofunsubstituted hydrazines, i.e., solutions of in NH NH have the addedadvantage of being free of carbon and their value as high energy fuelsis, therefore, enhanced.

Examples of compositions which are Within the scope of the invention areas follows, in which the various components are given as percent byweight of the total solution:

Compositions of the invention containing a hydraziniumdodecahydrododecahorate are prepared simply and directly by dissolving ahydrazinium polyhydrododecaborate in a hydrazine, employing thecalculated amounts of each component necessary to obtain a solution ofthe desired concentration.

A second and optional method consists in dissolving an acid (normally asa hydrate) of a polyhydrododecaborate of the formula H B H X (where X isa monovalent substituent, e.g., OH, NH and the like; and n is a cardinalnumber of 0-4, inclusive) in a hydrazine. The hydrazinium salt is thusformed directly in solution. Solution of the components in eitherprocess is accompreparing the final solution.

3 plished by simple stirring of a mixture of the components, employingheating, if desired, to expedite the process. Temperatures up to 100 C.or higher can be used.

A third method consists in dissolving an ammonium or substitutedammonium salt of the formula where R is hydrogen or lower alkyl, in ahydrazine and warming the mixture until ammonia or the trialkylamme isvolatilized from the mixture. To illustrate,

or [(C H NH] B H is mixed with NH NH and the mixture is warmed until allthe NHg or C H N is expelled. A temperature of at most 100 C. isgenerally suflicient to expel all the amines or ammonia. An ammonium orsubstituted ammonium polyhydrododecaborate bearing substituents bondedto boron can also be used as a reactant in this method.

Hydrazines which are employed as one reactant in the process are Wellknown compounds of the formula RRNNH as described earlier. Operablehydrazines include NH NH CH NHNH C H NHNH and the like. The hydrazinesneed not be anhydrous and usually they can be employed as purchased in90% or higher purity. The hydrazine employed to prepare the salt is notnecessarily the same hydrazine employed in To illustrate can bedissolved in NH Nl-l to obtain a composition of the invention.

Acids of polyhydrododecaborates and their hydrazinium salts are notgenerally available products. They are ob tained by reacting atrialkylamine-borane adduct of the general formula R NBH where the R"groups are lower alkyl, e.g., methyl, ethyl, propyl, and the like, witha boron hydride, e.g., B H and isolating the trialkylammonium salt. Thissalt can be used directly, as described previously, or it can beconverted to the free acid. The free acid is obtained by contacting asolution (aqueous or alcohol) of the trialkylammonium salt with acommercial acid ion-exchange resin and evaporating the solution soobtained to a point where the crystalline acid is obtained, generally asa hydrate. The acid can be dis solved directly, as described earlier, ina hydrazine or it can be neutralized with ammonia or ammonium hydroxideto obtain an ammonium polyhydrododecaborate. The preparation of arepresentative dodecahydrododecaborate salt and acid is described fullyin Example A.

The compositions of the invention include solutions of hydraziniumpolyhydrododecaborates which bear substituents bonded to theboron-containing group, e.g., -OH or NH Substitutedpolyhydrododecaborates are obtained by treating a salt of the B H anionor the acid, H B H with an appropriate reagent which results in replacement of hydrogen bonded to boron by an X group. To illustrate,polyhydrododecaborates bearing from 1-4 groups bonded to boron atoms areobtained as follows:

(1) A mixture of 3.0 g. of hydrated H B H (N.E., 154) and 1.75 g. ofoxalic acid is heated in a boiling water bath for 5 minutes withstirring. An exothermic reaction sets in and the temperature rises to120 C. with vigorous bubbling. The mixture is cooled to about 25 C. and5 ml. of water is added. The solution is neutralized with aqueous CsOHsolution to phenolphthalein end point. A precipitate forms and thereaction mixture is heated to boiling with addition of the minimumamount of water needed to dissolve the precipitate at the boiling point.The solution is cooled in an ice-water bath and the crystals which formare separated to obtain CS2B12H11OH. The cesium salt can be dissolved inwater and the aqueous solution can be passed through a column filledwith an acidic ion-exchange resin of the crosslinked polystyrenesultonicacid type. The aqueous efliuent can be neutralized with a hydrazine,e.g., NH NH and evaporated to dryness to obtain a hydrazinium salt, e.g.

which can then be dissolved in a hydrazine in the proper amount to forma composition with the desired proportions of salt and hydrazinecomponents.

(2) A reaction vessel is charged with a solution consisting of 20 g. ofNa B H -2H O and about 200 ml. of N-methyl-2-pyrrolidone. The solutionis stirred and 25 ml. of hydrochloric acid is added. The mixture isfiltered and the filtrate is distilled until a pot temperature of 205 C.is reached. The mixture is held at this temperature for 4 hours and itis then poured into 600 ml. of ethyl alcohol. The precipitate whichforms is separated by filtration. It is purified by dissolving inacetonitrile and reprecipitating with ethanol. The product is mixed with50 ml. of 6% aqueous NaOH solution, the mixture is refluxed for 4 hoursand then cooled. A portion of this mixture is evaporated to a smallvolume and a concentrated aqueous solution of CsOH is added. Theprecipitate which forms is separated, recrystallized from water anddried to obtain Cs B I-I (OH) This salt can be processed as described inthe preceding paragraph, designated (l), to obtain a hydrazinium salt,e.g., (NH NH B H (OH) from which hydrazine solutions of the desiredcompositions can be obtained by conventional processes.

(3) An aqueous solution of H B H is neutralized with a measured quantityof Be(OH) to provide a neutral solution of BeB H The solution isevaporated to dryness and the residue is dried intensively over P 0 toobtain BeB H -4H O. A portion of this salt is heated under very lowpressure over P 0 for 52 hours at 148 C. The dried product is suspendedin 100 ml. of water, 90 ml. of 1N NH OH is added with stirring, and themixture is filtered to remove Be(OH) The filtrate is evaporated todryness to yield (NH B H (OH) This salt can be processed as described ina previous paragraph, designated (1) to obtain a hydrazinium salt, e.g.,(NH NH B H (OH) from which hydrazine solutions of the desiredcompositions can be obtained.

(4) A reaction vessel is charged with 70 ml, of tert.- butanol and 6 g.of hydrated H B H i.e.,

The mixture is refluxed for 2 hours and water is added. The solution isboiled to remove the butanol as an azeotrope with Water. An aqueoussolution remains which contains the acid H B H (OH) The solution can beprocessed as described in the previous paragraph, designated (1) toobtain a hydrazinium salt, e.g.,

Compositions of the hydrazinium salt in a hydrazine can be prepared asdescribed earlier which have the salt and hydrazine in desired ratios.

Compositions which are illustrative of hydroxy-substituted dodecaboratesare:

20 (NH NH B H (OH) NH NH 22 (NH NH B H (OH) -78 NH NH and 15 (NH NH B H(OH) NH NH Polyhydrododecaborates bearing --NH groups as substituentsbonded to boron can be obtained by mixing the acid H2B12H12, alsoI'fiftil'red to as (H30)2B12H12, and formamide in aqueous solution. Thesolution is heated until water is removed completely and it is thenrefluxed. The solution is diluted with alcohol, e.g., CH OH, and it isthen neutralized with an aqueous solution of a hydrazine. Theneutralized solution can be evaporated to yield a solid hydraziniumpolyhydrododecaborate bearing NH groups bonded to boron. The solid saltcan be dissolved in a hydrazine to form a solution of the desiredcomposition, eg. 20% (NH NH B H NH and 80 NH NH The compositions of theinvention and their preparation are illustrated further in the exampleswhich follow.

Example A (A) A glass vessel is employed which is fitted with a stirrer,a thermometer and a reflux condenser which is also connected to a wettest meter. The vessel is charged with 200 ml. of triethylamine-boraneadduct prepared as described in US. 2,860,167. Nitrogen gas is passedinto the vessel and the reaction mass is heated to l70-175 C. A solutionof 29 g. of B H in 100 ml. of (C H NBH is added to the reaction massover a period of about one hour with vigorous stirring. After additionis complete, the reaction mixture is stirred minutes maintaining thetemperature at 170l75 C. Hydrogen gas is evolved at a rate whichdecreases sharply during the final stirring.

The reaction mass is cooled to about C. to form a mixture of white solidand pale yellow liquid. The solid is separated by filtration, washedwith ether and dried. Thfil'e 1S Obtalnfid g. of [(C2H5)3NH]2B12H12.

(B) A portion of this product is dissolved in water and the aqueoussolution is passed through a column filled with a commercial acidion-exchange resin of a crosslinked polystyrenesulfonic acid type. Theaqueous efliuent is a solution of H B H from which the free acid isobtained in solid form as a hydrate by evaporation of the solution. Thecrystalline acid may contain up to 10 or more molecules of waterhydration. Its exact composition is easily determined by conventionalanalytical procedures, e.g., titration of samples of known Weight. Thesolution can be neutralized with a base, e.g., NaOH or to obtain Na B Hor (NH4)2B12H12. The salts are isolated by evaporation of the solutionto dryness.

Example I A mixture is prepared consisting of one part of and about 2.5parts of 1,1-dimethylhydrazine. The mixture is heated at steam bathtemperatures for minutes. Ammonia is released as a gas and a solutioncontaining about 45% by weight of [(CH NNH B H in a)2 2 is obtained.

The bis(1,1 dimethylhydrazinium) dodecahydrododecaborate(2) is isolated,if desired, by evaporation of the solution at atmospheric pressure. Thecompound, which is a White crystalline solid, is recrystallized fromwater. It is obtained with one mole of (CH NNH as solvent ofcrystallization.

Analysis.-Calculated for B, 40.4; C, 22.1; H, 11.6. Found: B, 40.0; C,22.0, 21.4; H, 11.5.

Example II A portion of the aqueous efliuent containing H B H which isobtained as described in Example A, Part B, is neutralized withhydrazine hydrate to a pH of 7. The neutral solution is evaporated toleave (NH NH B H as a white crystalline solid. A solution of this saltin hydrazine is prepared in the ratio of 0.7 part of the salt to 2 partsof hydrazine (95% The solution is clear and it is heated for 10 minutesat steam bath temperatures (95-98 C.) with no evidence of decomposition.

The stability of the anion B H under the above conditions is shown bydiluting the hydrazine solution with water and adding an aqueoussolution of tetrapropyl- 6 ammonium bromide. The precipitate which formsis separated by filtration to obtain [(C H N] 1 H1 in substantiallytheoretical yield.

Example III A hydrate of H B H is dissolved in a small excess ofhydrazine hydrate. The solution is cooled and a crystalline saltseparates. The crystals are isolated and purified by crystallizationfrom water. The compound is dihydrazinium dodecahydrododecaborate(2)containing 2 moles of hydrazine of crystallization.

Analysis.Calcd for 2B 12H12 I B, 48.2; H, 11.0; N, 40.8. Found: B, 46.5;H, 11.0; N, 38.6.

Solutions are prepared containing, respectively, 075, 0.9, 1.1 and 1.2parts of the above salt in one part of hydrazine (%-k). These solutionscontain respectively 42%, 47%, 52%, and 54% by weight of hydraziniumsalt. The mixture containing 54% by weight of the salt requires slightwarming to obtain a clear solution. However, clear solutions with lessthan 54% by weight of (NH NH B H are obtained by simple mixing of thecomponents at prevailing atmospheric temperature (ca. 25 C.).

The solutions are stable against degradation or decomposition onprolonged heating, e.g., a solution containing about 43% by weight ofsalt [0.25 part of (NH2NH3)2B12H12 1H part of is heated at steam bathtemperatures (95-100" C.) for 2.5 hours with no evidence of reaction orbreakdown.

The solubility of a representative hydrazinium salt, i.e., (NH NH B H inhydrazine over a temperature range of 0 to 50 C. is shown in Table I,wherein the solubility is expressed as parts of H B H in parts ofsolution by weight).

TABLE I Solubility Temperature C.: (percent by weight of H B H O 22.0 1123.0 24.8 23.9 50 26.2

1 Density, 250/40:'1.0417.

The compositions of the invention are useful as monopropellants inliquid rocket propulsion motors. They can be used also in conjunctionwith minor quantities of oxidizing agents, e.g., nitrogen tetroxide,fluorine oxide, and the like to provide fuels with high specific impulseand high heats of combustion.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that this invention is not limited to the specificembodiments thereof except as defined in the appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A fluid composition comprising a hydrazine of the formula RR'NNHwherein R and R are groups selected from the class consisting ofhydrogen and lower alkyl, and a hydrazinium polyhydrododecaborate of theformula (RRNNH l3 H X, wherein R and R are defined as above, X is aradical selected from the class consisting of OH and NH and n is acardinal number of from 0 through 4.

2. A fluid composition of claim 1 wherein the hydraziniumpolyhydrododecaborate is (NH NH B H ,,X,,.

3. A fluid composition of claim 1 wherein the hydrazine 1S NHZNHZ.

4. A fluid composition of claim 1 wherein the hydrazine is NH NH and thehydrazinium polyhydrododecaborate i5 2N 3)2 12 12 11 11- 5. A fluidcomposition of claim 1 wherein n is O.

r are loweralkyland nis 0..

6. A process for preparing a fluid composition of claim 5 whichcomprises heating a compound of the formula (R NH) B H wherein R isselected from the class consisting of hydrogen and lower alkyl, with acompound of the formula RR'NNH wherein R and R are selected from theclass consisting of hydrogen and lower alkyl.

7. A fluid composition of claim 1 wherein the hydraziniumpolyhydrododecaborate is (NH NH B H 8. A fluid composition of claim 1wherein the hydrazine is NH NH and n is 0.

9. A fluid composition of claim 1 wherein R and R are hydrogen and n isO.

10. A fluid composition of claim 1 wherein R and R 11. Process whichcomprises reacting a compound of the formula (R "NH) B H wherein R" isselected from the class consisting of hydrogen and lower alkyl, with acompound of the formula RR'NNH wherein R and R are selectcdfrom theclass consisting of hydrogen and lower alkyl and isolating the resultingwherein R and R are defined as above.

References Cited by the Examiner UNITED STATES PATENTS CARL D.QUARFORTH, Primary Examiner.

REUBEN EPSTEIN, Examiner.

1. A FLUID COMPOSITION COMPRISING A HYDRAZINE OF THE FORMULA RR''NNH2WHEREIN R AND R'' ARE GROUPS SELECTED FROM THE CLASS CONSISTING OFHYDROGEN AND LOWER ALKYL, AND A HYDRAZINIUM POLYHYDRODODECABORATE OF THEFORMULA (RR''NNH3)2B12H12-NXN WHEREIN R AND R'' ARE DEFINED AS ABOVE, XIS A RADICAL SELECTED FROM THE CLASS CONSISTING OF OH AND NH2, AND N ISA CARDINAL NUMBER OF FROM 0 THROUGH 4.